John: Welcome to the forum.
I too am anything but a mystic. I'm an engineer turned scientist and first came across this topic after by chance reading Monroe's Journeys Out of the Body over 20 years ago. It was just sheer curiosity that got me reading the book when I happened to see it in a bookshop window. I figured the guy had either gone insane, or had stumbled onto something. So I put aside the tremendous tendency I had to think the former, and gave the latter a genuine try. Much to my surprise I began getting projection symptoms and I never looked back.
Problem was, when people like myself first started there were no groups such a these where we could all communicate and pass on hints and tips and so forth. So my progress was rather slow at first. You asked if the phenomenon is all to do with the mind. The answer to that is a resounding, yes. But I think what you are asking is the phenomenon merely something the physical brain concocts. In which case the answer is no (mind and brain are entirely different). Though I cannot provide you with independent proof of that fact. The best way is to discover for yourself and then decide.
Much has been written about this phenomenon over a great many years and it is all too easy to become sidetracked. But a good basic tip I give to people is that Astral Projection comes about by keeping your sense of conscious awareness awake, while you let your physical body just go to sleep as nomal. It's quite a tricky little mental balancing act to perform, and some are naturally better at it than others, but that is all you need basically do IMO.
The mental experiences people typically go through from attempting this have been isolated and labelled. Monroe (an engineer) was the pioneer in this work, so you might gain some benefit from studying the Monroe school. Bruce Moen (also an engineer) has taken Monroe's basic methods and simplified and modernised them yet further. So you may derive some benefit from his work also.
The other person I'd highly recommend, you already came across: Robert Bruce the author of Astral Dynamics. Robert takes a more traditional "obe" and "energy work" approach. These techniques generally lead you to having projections into what is known as the real-time zone. Where you typically end up looking down at your physical body whilst floating around your bedroom, etc. Whereas the other two are mainly concerned with projecting your conscious awareness into what are commonly called the Astral realms.
Within the Astral realms reside all manner of people in all kinds of circumstances, and it's quite fascinating being able to project within these places. You can sit and chat with these people, for example, in exactly the same way as you can on the Physical. (Well, those that are open to you that is.) You can discover other members of you Higher Self; visit the library within Focus 27; discover about your past lives, and so much else besides.
Perhaps the greatest thing about discovering all this within yourself, is you finally begin to understand the reasons how all the mystical side of life came about. The difference today, however, is we have a very much more evolved sense of consciousness. Which gives us a big advantage when trying to work it out.
Best of luck.
Yours,
Frank